Soft pinback

When wearing enamel pins, the metal clasp back that usually comes with them can get irritating after a while. These pinbacks are soft but grip the pin shaft well, holding them in place without irritating. Originally designed for the [Printables Flex It! (TPU Edition) contest](https://www.printables.com/model/1614716-soft-pinback).

#### Recommended Print Settings
- 0.4mm nozzle
- 0.15mm layer height
- 100% infill
- No supports
- Print as oriented
- TPU *only* (inflexible filaments will not hold)